This invention relates generally to improvements in bulldozers and the like. More particularly, but not by way of limitation, this invention relates to an improved blade support method and structure for use on bulldozers and the like.
Wherever used hereinafter, "pivot," "pivoting," etc. shall mean a moveable connection between two parts with only one degree of flexibility, such as a simple hinge; and "swivel," "swiveling," etc. shall mean moveable connection between two parts with at least two degrees of flexibility, such as a U-joint or ball and socket.
In general, bulldozer blade supports are arranged so that the blade can be raised and lowered, pitched about an axis that extends generally perpendicularly to the longitudinal axis of the bulldozer, and tilted about an axis that extends generally parallel to the longitudinal axis of the tractor. Most often, the blade is supported by a pair of relatively long beams or push arms that extend parallel to the longitudinal axis of the tractor and are swivel mounted on the tractor or track frame near the rear end thereof. Due to the length of the push arms, the blade is not well supported against lateral loads. It is necessary, therefore, to provide some form of stabilizing structure for supporting the blade against lateral forces.
Usually, raising and lowering of the blade, which is located at the front of the tractor, is accomplished by attaching one or more double-acting hydraulic cylinders to the tractor and to the push arms in an arrangement that permits substantially vertical movement of the blade as the push arms rotate on their mountings near the rear end of the tractor.
Pitching of the blade is generally accomplished by manual adjustment of a threaded strut or turnbuckle mounted on the push arms located on the side opposite a double acting tilt cylinder. One end of the cylinder and the strut is attached to a respective push arm and the opposite end thereof is pivotally attached to the blade so that the simultaneous extension and retraction of the strut and tilt cylinder causes the blade to pivot or "pitch" about its attachment to the push arms.
Tilting of the blade utilizes the tilt cylinder mentioned above. Extension and retraction of the tilt cylinder imposes a twisting force on the blade which causes one end of the blade to rise and the opposite end of the blade to fall. The desired angle of tilt may be attained by adjusting the force exerted by the tilt cylinder in cooperation with the strut. As will be appreciated, when tilting of the blade occurs, the effective distance between the points at which the push arms are attached to the trunnion decreases with respect to their attachment to the dozer blade and, thus, the trunnion ends of the push arms effectively move closer together. Accordingly, bending stresses occur in the push arms if the arms are rigidly connected to the blade such as by diagonals extending generally horizontally between the arms and the blade.
Various structural arrangements have been utilized in an effort to alleviate the problems caused by the bending forces induced when the blade is tilted and caused by the lateral loads. It should be pointed out that the severity of the bending forces in the arms is increased by the attempts made to stabilize the blade and push arm structure against lateral forces. In other words, attempts to support the blade against lateral movement and attempts to eliminate the bending stresses are somewhat at counter purposes.
One apparatus used to stabilize the blade against lateral forces is illustrated in U.S. Pat. No. 3,901,329 issued to Larry G. Eftefield on Aug. 26, 1975. A similar structure is shown in U.S. Pat. No. 3,941,195 issued Mar. 2, 1976 to Robert N. Stedman. The structure illustrated in those patents ties either the blade to the main frame of the tractor to avoid lateral instability or ties one of the push arms to the main frame to avoid the lateral instability. Although lateral stability is attained, extremely high forces are imposed on the tractor frame which themselves result in other difficulties.
An additional attempt that has been made to alleviate such lateral instability has been to extend diagonal braces from the push arms to the blade to make a rigid structure thereof. Such rigidity results in the imposition of bending stresses in the push arms where the diagonal braces are attached to the push arms. With such an arrangement, care must be taken in the design to provide adequate structure to support the combined forces of external lateral loads and of the bending stresses.
Accordingly, an object of this invention is to provide an improved support structure for blades on dozers and the like which provides the desired lateral stability while avoiding the imposition of bending forces thereon when the blade is tilted.